Heating liquids in vessels



Oct. I24, 1950 J. KNlvE'roN 2,527,430

HEATING LIQUIDs 1N vEssELs Filed April 18, 1946 Pafented oct. 24, 195o HEATING LIQUIDS vIN VESSELS James Kniveton, Wyncote, Pa., assignor to Selas ICorporation of America, Philadelphia, Pa., aV

corporation of Pennsylvania Application April 18, 1946, Serial No. 663,004V

This invention is concerned with heating liquid in vessels. y

It is an object of the invention to provide an improvement for heating liquids in vessels when a combustible iiuid fuelA is utilized as a source of heat, particularly to effect more uniform heating throughout a body of liquid contained in a vessel. I accomplish this by effecting combustion .of a combustible fluid fuel at a region below the bottom of the vessel so as to apply heat to the bottom of the liquid body contained therein,'and flowing or venting the heated gases generated and developedby such combustion in thermal exchange relation with the liquid body while out of physical contact with the liquid and the atmosphere. VMore particularly, the heated gases flow in thermal exchange relation with the body of liquid in such a manner that heat will be applied at distributed points about the outer portion of the liquid body throughout substantially its entire depth.

9 claims. (ci. 257-4) the liquid body in the vessel at a desired tempera- It is another object of the invention to procooling agent in heat exchange relation with the vessel when cooling of the liquid body is desired.

Further, in order to provide'several stages of cooling, provision may be made to-eifect initial cooling fof the liquid body by shutting off ,the supply of combustible uid fuel and delivering air alone to theregion at the bottom part of the vessel. Heat from the bottom part of the vessel is given up to such air which effects further cooling of the liquid body by owing in thermal eX- change relation therewith in paths ofv flow at the sides of the vessel. Such initial cooling by the air may be supplemented by additional cooling by the cooling agent, as previously explained, when this becomes necessary.

The above and other objects and advantages of the invention will be more fully understood from the following description taken in conjunction with the accompanying drawings forming a part of this specification, and of which Fig. V1 Vis' a vertical sectionalview more or less diagrammatically illustrating apparatus. embodying the invention for heating a vessel adapted to contain a body of liquid therein; and Fig. 2 is a View diagrammatically illustrating a control system embodying the invention for controlling the heating and cooling of the vessel of Fig. 1 to maintain ture or temperature range. Y

In Fig. 1 is shown heating apparatus embodying the invention comprising a vessel I0 adapted to contain a body of' liquid to be heated. The

vessel I0 is formed with a curved bottom I I which is secured at its peripheral edge portion-to a cylindrical-shaped side wall I2.' The side wall I2 extends below the bottom Il and, together with Aa base plate I4 which rests upon a suitable foundation I5, forms an outer shell or casing for a furnace construction or setting I6 for applying heat to the bottom I Ifof the vessel.l 'The furnace setting IB comprises a refractory lining Il including a horizontal refractory-wall section formed upon the base plate I4 and a Vertical .refractory i wall section formed-about the bottom part ofthe side wall I2.

The refractory lining I'I, an intermediate portion Vof the side wall I2 andi-the bottom II of the vessel 'form an enclosed furnace chamber I8 which is adapted to be fired to an elevated temperature in any suitable manner.y In the illustrated embodiment the furnace chamber I8 is fired by a plurality of gas burners I9 which are incorporated in the bottom wall section of the refractory lining I'I and to which a combustible gas mixture is supplied through conduits 2|.

In' order to provide a compact and' small furnace chamber I8, the burners are preferably of a short flame type, so that impingement of the verted to radiant heat which is projected from' the wall surfaces of the cavities to therbottom I I of the vessel. Such radiant heating of the bottom of the vessel Ill is augmented by convection heating by the heated products of combustion and radiant heating from the vrefractory'lining I'IV which is heated to incandescence bythe heated products of combustion sweeping over the inner surface of the lining.

In accordance with the invention, in order tol promote uniform heating of a body of liquid contained in the vessel IIJ, the heated gases in the furnace chamber I 8 are eiectively utilized to apply heat substantially uniformly about the outer part of the liquid body while heat is being applied to the bottom II of the vessel. I ac- 3 complish this by providing a plurality of Vertical tubes 22 which are distributed about the inside of the vessel I alongside of each other. The tubes 22 are disposed relatively close to the side Wall I2 and spaced therefrom to form a series of passages each of which is adapted to be conipletely enveloped by the body of liquid contained in the vessel I.

The tubes 22, which may be referred to as Vent tubes, extend downwardly through openings in the bottom II and the lower open ends thereof terminate a short distance above the vertical refractory wall section of the refractory lining I1. The heated gases, which are generatedand developed by combustion ofthe combustible gas mixture supplied to the burners I9, pass upwardly through the tubes 22 and discharge through the upper outturned ends thereof which extend through openings in the side wall I2. Inthis way the heated products of combustion are effectively utilized to applyv heat'substantially uniformly about the outer Apart of the liquid body throughout its entire depth, so that liquid at the regions'adjacent-to the side wall I2 may be heated at a rate approaching the rate at which heating Ofliquid isI effected adjacent to thev bottom I I of thev vessel. The heatedgases passing over the outer' surface of the bottom Il and flowing through the vent tubes 22 are out of physical contact with the` liquid in the vessel` I0 vand the atmosphere.`

When la fused salt or salt mixture is being heated in a vessel like the vessel I0, such a mixture may solidify when heating of the vessel is stopped'. When heating of the vessel is resumed and heat is applied only-to the bottom of the vessel, there is always'the danger ofv the salt or salt mixture melting very rapidly inthe bottom part of the vessel while the toppart thereof remains in a solid state. A In such case there is always-the likelihood ofthe vesselv failing at the bottom part thereof by reason of bulging that occurs due to expansion ofthe salt'or salt mixture in changing frommsolidto liquid phase.

The danger and likelihood of vessel failure is completely overcome in accord with the instant invention by flowing the heated products of combustion inconned paths of flow through the vent tubes y22 toheat the'outerportion of the solidifledv body which may be held inthe vessel I0. Since such heating ofthe outer part' of the solid mattei' is effected 'throughout its depth and at a rate approaching the rate at which heat is applied to the bottom part adjacent to the bottom I I, the vessel I0 will not be subjected to excessive localized pressures likely to cause-vessel failure.

Inorder to promote uniform heating of a body of liquid in the vessel I Il, an agitator of any well known type may be employed to circulate the liquid about the tubes 22. As shown in Fig. 1, such an agitator may comprise a plurality of suitable propeller blades 23 fixed to' an elongated shaft 24'driven through speed reducing gearing 25 from an electric motor 26 connected inany suitable manner (not shown) to a source of electrical supply.

'The speed reducing gearing 25 and motor 26 are carried on a support 21 which is angularly ad- 4 framework 32 which is secured at its lower end t the foundation I5.

When the liquid contained in the vessel I0 is to be heated to a high temperature, the bottom II, side wall I2 and tubes 22 may be formed of a suitable alloy steel, such as stainless steel, for example. Similarly, the blades 23 and driving shaft 24 therefor may also be formed of such an alloy steel to withstand the temperature' at which the body of liquid is maintained in the vessel I0.

The vessel I0 when formed of such alloy steel is especially useful as a so-called salt quench tank for quenching and cooling articles of ferrous metal from an elevated critical hardening temperature to effect hardening of the articles. In such case the liquid body, which may comprise afused salt or saltumixture, is maintained at a temperature considerably above the ambient temperature but below the critical hardening range. By keeping the fused salt or salt mixture ata ten'iperature'inA the neighborhood of 350 to 600 F., for example, and immersing in such liquid body articles of'ferrous lmetal which have previously beenheatedto the critical hardnening temperature of about 1500 F. or higher, for example, the quenching' and cooling of articles is carried out-at a slower rate than when the articles are cooled in-a single step fromthe critical hardening temperaturesubstantially tothe ambient air temperature.

After a uniform temperature 'is established throughout the articles while immersed in the fused salt bath, the; articles may be removed therefrom and air cooled.V Such quenching procedure is commonly referredv to as a delayed quench or an"interrup'ted quench, and is often employed for quenching and cooling alloy steels to produce certain physicald characteristics inv steel articles that cannot be obtained when quenching-is accomplished in asingle'step as, for example, by immersing the'heated articles directly in a4 body ofl unheatedf quenching oil or other suitable' quenching medium.

Inemployingthe apparatus of Fig. 1l for interrupted 'quenching of articles ofy ferrous metal, it is of considerable importance to maintain the quenching liquid` at a definite or desired'temperature or temperaturerange. After the body of liquid contained in the'vessel I 0 has initially been heated to such-a denite temperature and heated articles-of ferrous'm'etal areir'nmersed therein to effect hardening of the articles, the'temperature of the-body of liquid tends to rise and provision must be made for dissipating heat therefrom to keep the body of liquid at the desired temperature -or` temperature range.

In the embodimentf'illustrated this is accomplished by providing an annular-shaped metal shell-33 about thesvessel I0 which cooperates withl the side wall' I2 vto form an elongated vertical chamber 36'.; Thev chamber' {it-'extends downwardly fromv a region immediately beneath the upper outturned ends of'the'vent tubes 22 Vand at its lower end overlies the side refractory wall section of the refractory lining I'I.

A ring-shaped manifold 35 within the chamber 31% is fixedv in any suitable manner tothe upper part of shell 33. A suitable cooling agent, such as water, for example, is delivered from a source of'supply to the manifold 35'wl'1ich is formed with a' series `ofv openings 36 for directing the cooling agent against the outer surface of the side wall i2. flows downwardly over the side wall The cooling agent tricklesi and", I2 and' takes up heat from the liquid body inthe vessel ofthe cooling agent to the manifold 35, respon .Y

sive to the temperature of the liquid in thevessel I ll,y soV as to maintain the liquid body atv the desired temperature Yor temperature range.V Such a control system is more or less diagrammatically shown in Fig. 2 in which the cooling agent is delivered from a source of supply through Va conduit 38 to the manifold 35, and the combustible gas mixture is delivered to the burners I9 through conduits 2I and a main supply conduit 39 which receives a complete gas and air mixture from a` mixing device 4I. A cornbustible gas is supplied to the mixing device 4I from a suitable source of supply through a conduit 42 in which is provided a gas .pressure regulator 43, and combustion supporting air is supplied to the mixing device through a conduit 44 in which is provided a blower 45 arranged to be driven by an electric motor 45.

The control system of Fig. 2 for controlling the supply of combustible gas, combustion supporting gas and cooling agent, responsive to a thermal element 41 positioned within the Vessel IIJ, is so constructed and arranged that, when the liquid body is below a definite temperature, the supply of cooling agent to the manifold 35 is shut off and only a mixture of combustible gas and combustion supporting air is delivered to the burners I9.

When the temperature of the body of liquid rises above such definite value, cooling agent is not immediately supplied to the manifold 35. The desired dissipation of heat from the liquid body in the vessel I0 is effected in several steps and in the rst step the supply of combustible gas through the conduit 42 is shut off and air alone is supplied to the burners I9 by the blower 45. Such air, which is at the ambient temperature, immediately effectsv cooling of the burner cavities and refractory lining I'I to reduce the heating of vessel I0 by radiant heat.

The air delivered 'by the burners I9 into the furnace chamber I8 also sweeps overthe bottom II of'the vessel I9 and passes upwardly through the vent tubes 22, thereby taking up heat from the liquid body in the vessel.

In the event the air supplied to the burners I9 is insufficient to maintain the body of liquid in the vessel I at the desired temperature or temperature range and thetemperature of the liquid in the vessel tends to lrise further, cooling agent is then supplied to the manifold 35 through the conduit 38 to initiate the second cooling step so as to maintain the liquid body at'the desired temperature.

The above described operation of the atpparatus of Fig. 1 is accomplished by providing the thermal bulb 41 in the vesselI which is Y connected by a tube 48 to a suitable control description thereof is not believednecessary 6 Ifor an understanding of the invention described herein.

As shown in Fig. 2, the control device 49 is connected by a conductor 5U.` to one side of a source of electrical `supply.5|. The control device49 lis connected by conductors 52, 53 and v54 to an electromagnetically operable valve 55 which in turn isr connected by conductors 56,. 51 and 58 to the opposite side of` the source of electrical supply. Inthe event the temperature of a liquid in vessel I0 falls below a deiiniteVV value, the conductor 52 is energized to complete-J a circuit for the valve 55. With a further de-- crease .in temperature of the liquid in vessel.

I0 the circuit for the valve 55 is completed by condu-ctor53, andwith astill further decrease.I in temperature of the liquid the circuit for valve.- 55 is completed by the conductor v54. "The extent to which the valve 55 opens is dependent upon the fall in temperature of the liquid below the deiinite value, the opening of the valve being: smallest when conductor 52 is energized and greatest when conductor 54 is energized.

When valve 55 is energized by any one ofl conductors 52, V53 and' 54, a circuit is also com-- pleted for the motor 46, such circuit including I conductors 59 and 59 connecting the valve 553 to one terminal of the motor whose opposite terminal is connected by conductors El) and 59; to the source of electrical supply. Energzation of the motor 45 will start the blower 45 so that;

combustion supporting air will be delivered to the mixing device 4I through the conduit 44,.

the rate at which suchV air is delivered being f dependent upon the extent to which valve 55 is opened.

When valve 55 is energized a circuit is alsov completed for an electromagnetically operable combustion supporting air is supplied under pressure through 'the conduit 44 by the blower 45.

Theair supplied to the device 4I inspirates combustiblel gas into the device'from the conduit 42 when the valve 6I is open. AThe gas pressure: regulator 43 is preferably adjusted to reduce the pressure of' the combustible gas in conduit 42:

K substantially to atmospheric pressure. The rate ofiiow of combustible gas into the mixing device 4I is dependent upon the pressure and rate a which combustion supporting air is supplied to the device, so that a substantially complete com- 1 bustible mixture is always provided for the burners I9 by the mixing device. f

Hence, when the, liquid body contained in th vessel I0 is initially being heated and the thermal bulb 4'I calls for the maximum amount of supporting air at the maximum rate to the mixing device 4I. Underthese conditions the mixing device 4I supplies the combustible gas mixture at theV maximum rate t0 the burners I9 so that theV burners will operate at maximum capacity.

to, effect: heating of. the: vessel: IIJ .and the body of liquid contained therein.

As the .temperature ofthenliquid body rises and approaches the desired orderinite value, the. con.- trol device 49 acts to.. complete a ciicuit for the valve 55 through thev conductor. 53; When: this occurs the gas valve 6I. will remain.in.its.single open position. and the. air. valve 55.,.will close slightly so that. combustion` supporting air. will loe-supplied ata reduced rate to .the mixingdevice 4I.A Combustible gas will be inspirated. into the device 4I andmixwith-.the airand such mixture. will be delivered to. theburners I9 at a reduced rate so that the burners. will. operate at less than maximum capacity.

Uponfurther increase. intemperature of vthe liquidbody as it approachesthe. desired ordelf nitevalue, the control.: devicer 49. acts to complete a .circuit forthe valve 55 throughthe conductor 5 2. When this, occurs. thegas valvev 6I remains energized. and-in its, op,en.position, and valve 55pwill closefurtlierso that the combustible gas mixture will be suppliedV at a further reduced rate from the mixing device 4 I. Under these conditions the gasrnixture. will be supplied at the minimum rate tothe burners I9 and the latter will operate at minimum capacity to effect heating of the vessel I and the body of' liquid contained therein, Y

When the temperature of the liquid inthe vessel IU is at the desired or definite value,A the control dei/ice 49 acts to deenergize the conductors 52, 53- and 54, thereby deenergizing and clos,- ing the electromagnetically operable valves 55 and 6I to shut off the supplyof` combustible gas and combustion supporting air to the mixing device 4I. Deenergization. of fthe valve 55 opens the circuit for themotor 45.to" shut downl the blower 45.

In theevent the temperature-of the liquid in therrvessel I0 rises above the `desired' value the control device 49, inresponse to the expansible fluid thermostat oil which the thermal bulb 4'! forms a part, lacts to.A energize conductor 53.

Since the conductor 53 isconnected to conductor 54, this will energize the valve 55 so that air can be supplied at the maximum rate through the conduit 44. When the valve 55 is energized a .circuit is also completed. for motor 46 by theconductor 59 to render the blower 45 operative.

Since the coil of relay G4 is connected in con,- ductor 63, the energization of this conductor opens the normally closed 'contacts of: the relay so that, even though the conductor 54 isl energizedL-to complete a circuitfor the air valve 55, the conductor 59 will be opened andthe gas valve 6| will remain deenergized and closed. UnderV these-operating conditions onlyair willbe supplied by the blower 45to the burners I9. Suchv air, as explained above, effects cooling of the burner cav-n itiesZ and refractory lining Il to reduce the radiant heat received by thebottom II. In ad.- dition, the. cooling air supplied tothe furnace chamber I8 through the burners'qISisWeeps overV thebottom I I ofA thevessel and passes upwardlyA and 58 tothe source of electrical supply-5I. The@ energization of the valve 66 by conductor 65 opens such valve to an intermediate open position so that coolingagent will be supplied to the manifoldy 35.- In the event thetemperature o the liquid body in the vessel I0 still continues toI rise aboverthe desiredvalue, the control device 49;acts to energize conductor. 68 so that a circuit willbe completed for valve 65 whereby the latter will move from its intermediate openposi-Q.

tion; to. its wide open position to increase the ratev at which. cooling agent is supplied tofthe manifold 35.

Cross connections 69 and I9 are provided from conductors 68 and .65 to conductor 63'so that valve .willlremain in its wide open position and the blower. 45 will continue. to operate. during the periods when cooling agent is being supplied to the manifold. 35. In this way cooling air will be supplied to the: furnace chamber I8 and pass through the vent tubes 22 while cooling agent is flowing downwardly. on .the outer surface of the side wall I2 from themanifold 35, thereby effectingV rapid cooling of liquid in. the vessel I0 to cause its temperature to fallito the desired or definite value.

In view of the foregoing, it shouldnow beunderstood that by providing the vent tubes 22, theheated gases passing therethrough from the furnace chamber I8 promote uniform heating of body of liquid adapted to be held in the vessel i0, so that the outer portion of the liquid body throughout its depth may be heated at approximately the same iate as the part of the liquid body adjacentto. the bottom II of the vessel ID. Heat transfer is effected to the liquid by. conduction through tlie Walls of the tubes 22 from the heated gases passing through thelatter. Uniform heating of the liquid. body is further promoted byforced circulation of the liquid in the vessel Hlby theV propeller blades 23. Moreover, the control system described and shown in Fig. 2 eectively maintains the liquid in the'. vessel I0 at thedesiized temperature or'temperature range.

While; only a single row of burners I9 is shown in the apparatus of Fig. l, it should be understood that several rows of burners may beprovided and arranged in .any desirable manner to effect thev desired. heating' at th-e bottom II of.

.the vessel ill. l Moreover, the burners may. be arvushownfor igniting the burners i9 followingv a shutdown. period.. However, such ignition.- devices are Well. knowninthe art and it should be understood that 'in practice provision would normally be madeto include 'an automatic ignitiony deviceforthe burners I 9.

While a single embodiment'v of: the invention has been-shown and described, such variations and modications arev contemplated' which fall within the true spirit and scope of the invention,

as pointed out in the following claims.

What is claimed is:

l. In the artoft heating and cooling a body of liquidA in a vessel,. the improvement which comprises burning fluid fuel beneath the vessel in a space partly dened by the Vbottom of the vessel and causing the heated'gasesgeneratedandde veloped by said combustion to ow in one or more pathsfin thermal exchange relation with the body.'

of liquid out of physical contact with the liquid and the atmosphere when heating of the liquid is desired, and delivering a gaseous cooling medium to the space and causing such cooling medium to flow in said one or more paths when cooling of the liquid is desired.

2. In the art of heating and cooling a body of liquid in a vessel having a bottom and a side wall extending upwardly therefrom, the improvement which comprises burning iiuid fuel beneath the vessel in a space partly defined by the bottom of the vessel and causing the heated gases generated and developed by said combustion to flow in thermal exchange relation with the body of liquid and out of physical contact with the liquid and the atmosphere so as to apply heat to the body of liquid substantially'about'the entire outer portion thereof adjacent the side wall when heating of the liquid is desired, and causing a liquid cooling agent to flow along the outer'surface of the side wall when cooling of the liquid in the `vessel is desired.

3. In the art of heating and cooling a body of liquid in a vessel, the improvement which cornprises burning uid fuel so as to produce heated gases at an elevated temperature and causing such heated gases to flow in one or more paths in thermal exchange relation with the body of liquid and out of physical contact with the liquid and the atmosphere when heating'of the liquid is desired, causing a Agaseous cooling medium toV ow in said one or more paths when cooling of the body of liquid is desired, and causing a liquid cooling agent to flow in thermal exchange relation and out of physical Contact with the body of liquid when additional cooling-cf the liquid in the vessel is desired.

4. Heating and cooling aparatus comprising a vessel adapted to hold a body of liquid, said vessel having a bottom and a side wall extending upwardly therefrom, structure including said bottom providing a closed furnace chamber, said bottom forming a roof for the chamber, gasred burner means to effect `combustion of a mixture of a combustible gas and air for firing the chamber to an elevated temperature, means providing a passage for venting heated gases from the chamber, said lastmentioned meansV being so constructed and arranged that the heated gases vented through the passage flow in heat exchange relation with the body of liquid, a device for mixing the combustible gas and air, supply means for delivering the combustible gas and air to said device and the mixture from the latter to said burner means, cooling meansV for owing a liquid cooling agent in thermal exchange relation and out of physical contact Withthe body of liquid, conduit means for supplying the cooling agent to said cooling means. and sequentially operated means for controlling the supply of the gas mixture to said burner means by said delivery means and the supply of cooling agent to said cooling means through said conduit meansin response to the temperature of said Vessel.

5. Heating and cooling apparatus comprising a vessel adapted to hold a body of liquid, said vessel having a bottom and a side wall extending upwardly therefrom. structure including said bottom providing a closed furnace chamber, said bottom forming a roof for the chamber, gas-fired burner means to effect combustion cfa mixture of a combustible gas and air for ring the chamber to an elevated temperature, means providing one or more passages for Venting heated gases from the chamber, said last-mentioned means being so constructed and arranged that the heated gases lo vented through the passage or passages ow in heat exchange relation with the body of liquid, a device for mixing the combustible gas and air, supply means for delivering the combustible gas and air to said device and the mixture from the latter to said burner means, cooling means for flowing a liquid cooling agent in thermal exchange relation and out of physical contact with the body of liquid, conduit means for supplying the cooling agent to said cooling means, and temperature responsive means for shutting off the supply of combustible gas to said burner means by said delivery means when the body of liquid in the vessel reaches a desired temperature and permitting ow of cooling agent to said cooling means through said conduit means when the body of liquid in the vessel rises above the desired temperature.

6. Heating and cooling apparatus comprising an open vessel having a bottom and side walls extending upwardly therefrom, structure including said bottom forming a closed combustion cham-` ber, means to supply a combustible fuel mixture to said chamber to be burned therein, Vent means for the products of combustion forming a plurality of passages passing through vsaid bottom and adjacent to said side Walls and through said side walls near the top thereof to the atmosphere,

structure forming a chamber around said side Walls, means located in said chamber to supply a cooling medium to said side walls, means responsive to the temperature of material in said vessel, means to control the supply of fuel, means to control the supply of cooling medium, and means operated by said temperature responsive means to adjust said two control means to reduce the supply of fuel and then increase the supply of cooling medium as the temperature of the material in said vessel increases.

'7. Heating and cooling apparatus comprising a vessel adapted to hold a body of liquid, said vessel having a bottom and side wallsextending upwardly therefromy structure including said bottom forming a closed combustion chamber formed below said vessel, burners located in said cham-v ber, means for supplying gas to said burners, means for supplying air to said burners, the gas and air burning in said combustion chamber, Vent means extending through the bottom of said Vessel and through the liquid therein to the atmosphere through which the products of combustion pass, means responsive to the temperature of the liquid in said vessel, and mechanism operated by said last-mentioned means to cut 01T the supply of gas to said burners in response to increase in the temperature of said liquid, the air continuing to now to said burners to cool them and the combustion chamber and through said vent means to cool said liquid.

8. Heating apparatus comprising an open vessel having a bottom and side Walls extending upwardly therefrom, structure including said bottom forming a closed combustion chamber, burner means through which a combustible fuel mixture is supplied to said chamber to heat said vessel, a plurality of venting tubes for the products of combustion, said tubes being located around the inside of said side walls of said vessel with their lower ends extending through said bottom 'and into said combustion space and the upper ends of said tubes extending through said side walls near the top thereof whereby material near the side walls of said vessel will be heatedv by said tubes, structure forming a chamber around said side Walls below the upper ends of said tubes, and means located in said chamber to supply a cooling medium to lsaid side walls.

9. Heating apparatus comprising an open vessel having a bottom and side walls extending upwardly therefrom, structure including said bottom forming a closed combustion chamber, means to Ysupply a combustible fuel mixture to said chamber to be burned therein, vent means for the Aproducts of combustion forming a plurality of Ypassages passing through said bottom and adjacent to said side Walls and through said side vWalls near the top thereof to the atmosphere,

structure forming a chamber surrounding said side walls, and means located in said chamber to supply a cooling medium to said side Walls.

JAMES KNIVETON.

.REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

